Column agglutination technology (CAT) employs an immunodiagnostic test element, such as a cassette or card, that includes or supports a plurality of columns or chambers. A quantity of beads which are typically made from glass or similar material or, alternatively, a gel matrix are added to the columns of the test element along with a suitable reagent prior to the addition of a patient sample, such as whole blood, plasma, serum, or red blood cells. An agglutination reaction can then be created in each test chamber followed by centrifugation or agitation of the test element, thereby enabling blood typing or other tests. During centrifugation, large agglutinants are trapped above the beads while smaller agglutinants are trapped along the length of the column, within the beads or gel matrix, and smaller red blood cells (RBCs) pass therethrough toward the bottom of the column. Examples of test cassettes employing CAT are described in U.S. Pat. Nos. 5,338,689 and 5,863,802, each herein incorporated by reference in their entirety.
Efficient manufacturing of column agglutination test elements requires that the glass beads used therein be able to flow freely during a manufacturing fill step when the glass beads are initially dispensed into each of the test columns. Following their manufacture, and as received from suppliers, the glass beads typically have adequate flow rates. However, the beads also include various impurities, such as dust, oils and soda ash, which would prevent overall consistency in use. Therefore, the beads are washed prior to filling the columns of a test element. Though the washing operation removes the impurities, this process also produces attractive forces between the beads that can significantly retard the flow rates of the beads and impact manufacturing time in filling the chambers of a test element.
Type I borosilicate glass beads of approximately 50-120 μm diameter are typically used in the manufacture of column agglutination test elements. The clean smooth surface of the beads causes each bead to associate, or cohere, to adjacent beads at their contact points. This cohesion force negatively impacts the ability of the beads to flow. Thus, there is a need to enhance flow rates of cleaned glass beads and to minimize the variability of flow rates among different batches of cleaned beads in order to reduce manufacturing machine downtime.